This application is related to commonly-assigned, concurrently filed, U.S. patent application Ser. No. 08/570,055.
The invention relates to polymer-containing compositions, particularly structural adhesive compositions. S. R. Hartshorn in Structural Adhesives, Chemistry and Technology, Plenum, 1986 (ISBN 0-306-42121-6) lists three definitions for "structural adhesive" on page 2--(I) "thermosetting resin compositions used to form permenant, load-bearing, joints between two rigid, high-strength, adherends;" (2) "a bonding agent used for transferring required loads between adherends exposed to service environments typical for the structure involved;" and (3) "greater than 1,000 psi tensile shear strength measured by the ASTM D-1002 procedure." As used herein, "structural adhesive" can be any adhesive that meets at least one of these definitions.
One application area for structural adhesives is in the bonding of lightweight metal and plastic materials in the fabrication, repair and reconstruction of automotive and truck vehicle bodies and component parts. The use of elastomers in structural adhesives to improve low temperature properties, such as impact resistance, is well known. While both solid gum and liquid elastomers can be utilized for this purpose, the limited solubility and greater incompatibility of the solid elastomers can restrict their use, especially at higher levels of elastomer concentrations.
U.S. Pat. No. 4,769,419 describes an acrylic adhesive composition that includes a urethane-modified olefinic-terminated liquid elastomer. The precursor for producing the novel elastomer is derived by reacting olefinic monoepoxide compounds (e.g., glycidyl methacrylate) with polycarboxylic homopolymers or copolymers of conjugated dienes having from 4 to 12 carbon atoms (e.g., carboxylated polybutadiene). According to Examples 1-3, 1,8-diazabicyclo[5.4.0]undec-7-ene is used as a catalyst for reacting carboxyl-terminated polybutadiene liquid rubber and glycidyl methacrylate. The precursor compound is reacted with a monoisocyanate (phenyl isocyanate) to produce the novel elastomer. An acrylic structural adhesive composition is described that includes the novel elastomer.
Although the liquid elastomers described in U.S. Pat. No. 4,769,419 have proven to be very useful, they do have a few drawbacks. They exhibit a sufficiently high viscosity such that a diluent is required during their commercial production. The presence of a diluent increases the complexity and cost of producing and using the liquid elastomer and contributes to the odor of the adhesive that includes the liquid elastomer. A less expensive liquid elastomer that has a lower viscosity so that a diluent is not required at least during commercial production would be very desirable.
Polybutadiene elastomers have been modified to include various terminal or pendant groups for various purposes. One class of modified polybutadienes is liquid vinyl- or olefinic-terminated polybutadienes. For example, U.S. Pat. Nos. 3,910,992 and 3,925,330 describe reacting a carboxyl-terminated polybutadiene with glycidyl acrylate to obtain a liquid vinylidene-terminated polymer of the structure: EQU CH.sub.2 .dbd.C(R)--A--C(OH)(R)--CH.sub.2 --O--C(O)--(--B--)--C(O)--O--CH.sub.2 --C(OH)(R)--A--C(R).dbd.CH.sub.2
wherein A is preferably a bivalent radical of the structure --CH.sub.2 --O--C(O)-- and B is a polybutadiene backbone. A tertiary amine is the preferred catalyst.
U.S. Pat. No. 3,897,514 discloses a process for curing hydroxy-terminated prepolymer to rubber that includes mixing a hydroxy-terminated polybutadiene prepolymer with a curing system comprising a cyclic anhydride and a di- or tri-functional epoxide. The curing catalyst is a chromium salt. The epoxides are diglycidyl ether epoxides, cyclic aliphatic diepoxides and triepoxides. The resulting product is cured and is a solid.
U.S. Pat. No. 4,156,700 discloses a propellant additive that is a prepolymer derived from reacting hydroxyl-terminated polybutadiene and an anhydride. According to Example 1, a mixture of 1420 g (1.00 eq) hydroxyl-terminated polybutadiene (R45M from Arco Chemical), 100 g (1.0 mole) succinic anhydride and benzene are heated under reflux conditions for 48 hours. After evaporation of the solvent the viscosity of the resulting product is reported to be 180 poises at 25.degree. C. According to Example III, a mixture of 154 g (1 eq.) cis-1,2-cyclohexanedicarboxylic anhydride and 1420 g (1 eq.) R45M polybutadiene is heated at 90.degree. C. for 66 hours. The resulting product is reported to have a viscosity of 374 poises at 25.degree. C.
U.S. Pat. No. 4,857,434 discloses a liquid methacrylate terminated polymeric hydrocarbon maleate prepolymer having pendant maleate groups. This prepolymer is obtained by a multi-step synthesis that includes two separate maleation reactions (i.e., there are two steps of reacting an intermediate with maleic anhydride).
The first step involves the reaction of a functionalized liquid hydrocarbon polymer having hydroxyl, thiol or amine terminal groups "with an unsaturated carboxylic acid anhydride" to provide a maleate. The structure given in column 4 for the unsaturated carboxylic acid anhydride reactant includes a C.dbd.C bond in the heterocyclic ring. The reaction of 2 moles of maleic anhydride with each mole of hydroxyl terminated polybutadiene is presented as an example. The reaction product structure shown in column 3 includes a C.dbd.C bond outside the polybutadiene core backbone. The reaction "is preferably carried out in the presence of a thermal inhibitor such as di-t-butyl cresol" and, "although no catalysts are necessary", phosphoric acid and stannous octoate are mentioned. "The reactants are usually added in approximately stoichiometric amounts so that each functional group, e.g., a hydroxyl on the polymer, can react with one maleic anhydride molecule".
The second step involves reacting the maleate with a reagent containing a methacrylate group. Glycidyl methacrylate is mentioned as a methacrylate-containing reagent. A catalyst is not necessary, but triethylamine is mentioned as one catalyst useful for reducing reaction time and temperature.
The third step involves reacting maleic anhydride with the hydroxyl groups generated by the previous reaction with glycidyl methacrylate to provide pendant maleate groups.
The prepolymer by itself or with mono- or multi-functional unsaturated monomers (such as a reactive acrylic or methacrylic diluent) and with either a thermal or photoinitiator on exposure to heat, UV or high energy ionizing radiation forms a cured material that is said to be useful as an adhesive.
JP-B-94017451, according to an English translation, discloses a flexible resin composition that is made by mixing an epoxy resin and the product of an "alkenyl anhydrous succinic acid" reacted with a hydroxy-terminated polybutadiene. The epoxy resin component typically is a diepoxide such as bisphenol A diglycidyl ether, although the possibility of a liquid mono-epoxy resin also is mentioned. The resin composition is said to be useful for insulation.
JP-B-92055453; according to an English translation, discloses a rubber composition that includes a solid rubber and the product of a liquid diene copolymer having a terminal hydroxyl group reacted with an "alkenyl anhydrous succinic acid". The diene/alkenyl anhydrous succinic acid reaction can be carried out at 10.degree.-200.degree. C., 1-10 atms and 0.5-24 hours. The "alkenyl anhydrous succinic acid" is provided in an amount greater than necessary to react all of the hydroxy groups.